/*
 * prng.c
 *
 * pseudorandom source
 *
 * David A. McGrew
 * Cisco Systems, Inc.
 */
/*
 *
 * Copyright(c) 2001-2006 Cisco Systems, Inc.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 *   Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 *
 *   Redistributions in binary form must reproduce the above
 *   copyright notice, this list of conditions and the following
 *   disclaimer in the documentation and/or other materials provided
 *   with the distribution.
 *
 *   Neither the name of the Cisco Systems, Inc. nor the names of its
 *   contributors may be used to endorse or promote products derived
 *   from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 */

#include "prng.h"

/* single, global prng structure */

x917_prng_t x917_prng;

err_status_t x917_prng_init(rand_source_func_t random_source) {
    v128_t tmp_key;
    err_status_t status;

    /* initialize output count to zero */
    x917_prng.octet_count = 0;

    /* set random source */
    x917_prng.rand = random_source;

    /* initialize secret key from random source */
    status = random_source((uint8_t *) &tmp_key, 16);
    if (status)
        return status;

    /* expand aes key */
    aes_expand_encryption_key(&tmp_key, x917_prng.key);

    /* initialize prng state from random source */
    status = x917_prng.rand((uint8_t *) &x917_prng.state, 16);
    if (status)
        return status;

    return err_status_ok;
}

err_status_t x917_prng_get_octet_string(uint8_t *dest, uint32_t len) {
    uint32_t t;
    v128_t buffer;
    uint32_t i, tail_len;
    err_status_t status;

    /*
     * if we need to re-initialize the prng, do so now
     *
     * avoid overflows by subtracting instead of adding
     */
    if (x917_prng.octet_count > MAX_PRNG_OUT_LEN - len) {
        status = x917_prng_init(x917_prng.rand);
        if (status)
            return status;
    }
    x917_prng.octet_count += len;

    /* find out the time */
    t = (uint32_t) time(NULL);

    /* loop until we have output enough data */
    for (i = 0; i < len / 16; i++) {

        /* exor time into state */
        x917_prng.state.v32[0] ^= t;

        /* copy state into buffer */
        v128_copy(&buffer, &x917_prng.state);

        /* apply aes to buffer */
        aes_encrypt(&buffer, x917_prng.key);

        /* write data to output */
        *dest++ = buffer.v8[0];
        *dest++ = buffer.v8[1];
        *dest++ = buffer.v8[2];
        *dest++ = buffer.v8[3];
        *dest++ = buffer.v8[4];
        *dest++ = buffer.v8[5];
        *dest++ = buffer.v8[6];
        *dest++ = buffer.v8[7];
        *dest++ = buffer.v8[8];
        *dest++ = buffer.v8[9];
        *dest++ = buffer.v8[10];
        *dest++ = buffer.v8[11];
        *dest++ = buffer.v8[12];
        *dest++ = buffer.v8[13];
        *dest++ = buffer.v8[14];
        *dest++ = buffer.v8[15];

        /* exor time into buffer */
        buffer.v32[0] ^= t;

        /* encrypt buffer */
        aes_encrypt(&buffer, x917_prng.key);

        /* copy buffer into state */
        v128_copy(&x917_prng.state, &buffer);

    }

    /* if we need to output any more octets, we'll do so now */
    tail_len = len % 16;
    if (tail_len) {

        /* exor time into state */
        x917_prng.state.v32[0] ^= t;

        /* copy value into buffer */
        v128_copy(&buffer, &x917_prng.state);

        /* apply aes to buffer */
        aes_encrypt(&buffer, x917_prng.key);

        /* write data to output */
        for (i = 0; i < tail_len; i++) {
            *dest++ = buffer.v8[i];
        }

        /* now update the state one more time */

        /* exor time into buffer */
        buffer.v32[0] ^= t;

        /* encrypt buffer */
        aes_encrypt(&buffer, x917_prng.key);

        /* copy buffer into state */
        v128_copy(&x917_prng.state, &buffer);

    }

    return err_status_ok;
}

err_status_t x917_prng_deinit(void) {

    return err_status_ok;
}
